1. Field of the Invention
The present invention relates to a numerical controller for controlling a machine tool or the like and, more particularly, to a numerical controller with a novel system configuration of sensors and servo motors that use signals from the sensors.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating the main elements of a system in which a numerical controller controls a machine tool or the like in one conventional mode. The numerical controller (CNC) 10 comprises a numerical control section 11 and a motor control section 12 that controls motors.
Following a machining program or the like, the numerical control section 11 outputs movement commands for individual motors to a motor control section 12. The motor control section 12 uses the commands to perform control functions such as position loop control and velocity loop control, generate pulse width modulation (PWM) signals for rotating the individual servo motors, and output the PWM signals to servo amplifiers 20, 21, 22, . . . for the corresponding servo motors. Servo amplifiers 20, 21, 22, . . . rotate respective servo motors 30, 31, 32, . . . according to the PWM signals.
Encoders 40, 41, 42, . . . attached to respective servo motors 30, 31, 32, . . . sense the rotational positions or rotational speeds of servo motors 30, 31, 32, . . . . The sensed rotational positions or rotational speeds of servo motors 30, 31, 32, . . . are fed back to the motor control section 12 in the CNC through servo amplifiers 20, 21, 22, . . . for use in position loop control or velocity loop control.
Tables and other movable parts driven by servo motors 30, 31, 32, . . . are provided with sensors S1, S2, S3, . . . that sense the positions of the respective movable parts. Signals from sensors S1, S2, S3, . . . are fed back to the CNC 10 through servo amplifiers 20, 21, 22, . . . , respectively. If sensors S1, S2, S3, . . . are linear scales that sense the positions of the tables or other movable parts, the motor control section 12 performs feedback control concerning the positions of the movable parts on the basis of the feedback signals from these sensors. The correspondence among sensors S1, S2, S3, . . . , servo amplifiers 20, 21, 22, . . . , and motors 30, 31, 32, . . . is fixed and unchangeable.
FIG. 2 shows the configuration of another conventional numerical controller system, in which a plurality of servo amplifiers 20, 21, 22, 23, and a plurality of interface units 50, 51, . . . are daisy-chained to a numerical controller (CNC) 10 through a serial bus. Also connected to interface units 50, 51, . . . are sensors S1, S2, S3, . . . , such as linear scales that sense the positions of servo motor driven tables and other movable parts, sensors that sense temperatures, pressures, voltages, currents, and other quantities, and limit switches.
Signals sensed by sensors S1, S2, . . . are sent to the CNC 10 through interface units 50, 51, . . . . The CNC 10 receives the signals from sensors S1, S2, . . . sequentially, identifies the sensor signals according to their order of reception, and relates the sensors S1, S2, . . . to the servo motors 30, 31, . . . . Sensors S1 to S4 are, for example, linear scales, sensor S1 sensing the position of the movable part driven by servo motor 30, sensor S2 sensing the position of the movable part driven by servo motor 31, sensor S3 sensing the position of the movable part driven by servo motor 32, and sensor S4 sensing the position of the movable part driven by servo motor 33. The motor control section 12 then uses the signal from sensor S1 for the position loop control of servo motor 30. Likewise, the motor control section 12 uses the signals from sensors S2, S3, S4 for servo motors 31, 32, 33, respectively. These correspondences are fixed.
When a movable table or another part of a machine tool must move at high speed or the machine tool is large, a large torque is required. In this case, a plurality of servo motors may be used to drive the table or the other part. Although the table or the other part is driven by a plurality of servo motors, a single sensor (linear scale) is attached to it for sensing its position or speed, creating a need to share the signal sensed by the linear scale among the plurality of servo motors. Another need is to share emergency stop signals and other signals from the machine among a plurality of servo amplifiers and servo motors.
In the system in FIG. 1, however, the linear scales or other sensors correspond to the servo motors on a one-to-one basis, preventing the use of signals from a single sensor for the control of a plurality of servo motors. The system in FIG. 2 allows the associations between servo motors and sensors to be changed, but does not allow signals from a plurality of sensors to be used by a single servo motor, nor does it permit signals from a single sensor to be used by a plurality of servo motors. Therefore, signals from sensors used by other servo amplifiers cannot be used directly.
To enable the use of signals from other non-assigned sensors in this system, the motor control section 12 has to transfer signals from one servo motor to another, hindering the high-speed control required for servo motors 30 to 33.